Printed circuit board including waveguide and method of producing the same

ABSTRACT

Disclosed is a PCB in which a waveguide is embedded, and a method of producing the same. The PCB includes a substrate, and a lower clad layer formed on the substrate through a predetermined process to allow an optical signal irradiated thereto to be total-reflected thereby. A core layer is formed on the lower clad layer through a predetermined process and exposed using an exposing film on which a waveguide pattern is formed to form the waveguide with a predetermined shape therefrom. Furthermore, an upper clad layer is formed on the core layer through a predetermined process to allow the optical signal irradiated thereto to be total-reflected thereby.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains, in general, to a printed circuit board(PCB) including a waveguide, and a method of producing the same. Moreparticularly, the present invention relates to a PCB in which variousshapes of waveguides for a large surface are embedded, and a method ofproducing the same, in which a core layer cured by UV (UV) and a cladlayer are coated on the PCB and the core layer is then exposed using anexposing film on which a waveguide pattern is formed. Additionally, thepresent invention provides a multi-layered PCB including waveguidesembedded therein and a method of producing the same, in which a prepregis interposed between the waveguide-embedded PCBs to conduct a layup ofthe PCB and a viahole are then formed and copperplated to electricallyconnect layers constituting the resulting PCB to each other.

2. Description of the Related Art

Generally, a PCB is used as critical parts of electric and electronicproducts for connecting electronic parts to each other along a circuitpattern designed on a substrate or supporting the electronic parts, andacts as a passive component widely used in home appliances,communication devices, and industrial devices.

In this regard, a method of producing the PCB includes attaching a thinfilm made of a predetermined metal such as copper to one side of aphenol resin or an epoxy resin dielectric substrate, etching the thinfilm (the remaining portion of the thin film except for a linear circuitpattern is etched and removed) to form a predetermined circuit, andforming holes through the thin film to mount parts on the substrate.

The PCB may be classified into a single-sided PCB, a double-sided PCB,and a multi-layered PCB according to the number of sides of the PCB inwhich the circuit pattern is formed. At this time, the higher the numberof layers constituting the PCB is, the higher the number of partsmounted on the PCB is. Thus, the multi-layered PCB may be adopted inhigh precision electronic products. The single-sided PCB includes aphenol resin as the substrate, and is used in products such as a radio,a telephone, or a simple-structured instrument, in which a circuitpattern is not complicated. Additionally, the double-sided PCB includesan epoxy resin as the substrate, and is applied to electronic productssuch as a color TV, a VTR, and a facsimile, in which a circuit patternis relatively complicated. Furthermore, the multi-layered PCB means aprint wire substrate in which conductive patterns are formed on three ormore layers including a surface conductive layer, and in which thelayers are separated from each other by dielectric films positionedbetween the layers. The multi-layered PCB is applied to high precisiondevices such as computers with 32 bits or more, electronic switchboards,or high performance communication devices.

Meanwhile, a flexible PCB is used in case that a circuit board must bemoved because it is applied to automated devices or camcorders, and thecircuit board must be bent when parts are mounted on the circuit board.

Currently, a transmission speed of a signal of an electronic device isconsidered as an important parameter according to advances in computerand communication technologies, thus the precision alignment ofimpedances between parts and circuit patterns in a high frequency PCBbecomes vital.

The high frequency PCB is limited in transmitting a large volume of dataat an ultra-high speed because a circuit acting as a transmission mediumis made of a conductive metal such as copper. To avoid the above limit,an optical PCB is developed, in which a waveguide with a predeterminedsize is directly formed on a silicone substrate and the resultingsilicone substrate is embedded in a PCB.

In other words, the optical PCB includes the waveguide made of a polymeror a glass fiber embedded therein to transmit and receive a beam actingas a signal therethrough unlike a conventional PCB in which a copperplate is patterned to form an inner layer and an outer layer thereof.

In the optical PCB, an electrical and an optical signal are all used,and the ultra-high data communication is interfaced by the opticalsignal. Additionally, a copper circuit pattern is formed in an elementto convert the optical signal into the electrical signal to store dataand to treat the electrical signal, and a glass plate as well as thewaveguide is embedded in the optical PCB.

However, in case that the waveguide is formed on the silicone substrateand the resulting silicone substrate is embedded in the PCB to form theoptical PCB, the waveguide for a large area cannot be formed and it isdifficult to conduct the application through the formation of thecircuit due to a size of the silicone substrate of 8 to 12 inches.

Further, in the above case, it is impossible to form various shapes ofwaveguides in the PCB.

Meanwhile, the optical PCB may be applied to a switch and a transceiverof a communication net, a switch and a server of a data communication, acommunication device of the aerospace industry and an avionics, a basestation of a mobile telephone of a universal mobile telecommunicationssystem (UMTS), or a backplane and a daughter board used in amainframe/supercomputer.

Additionally, the rapid increase of use of the Internet and theimprovement of the service quality on the Internet led to the increasein a quantity of data treated and transmitted, thus the optical PCBacting as a medium capable of conducting an optical-interfacing isdeveloped to extend a bandwidth and increase a treating speed of thesignal. In other words, in the conventional PCB, the optical-interfacingwithout being affected by the EMS (electro magnetic susceptibility)characteristic is needed because the electrical signal is limited by theEMS characteristic during a high-speed switching at a GHz range of thebandwidth.

However, even though ten years have passed since the optical PCB wasdeveloped, a first and a second EOCB (electrical-optical printed circuitboard) technology in which a backplane treats a signal in apoint-to-point manner against a glass fiber, and a third EOCB technologyof an optical signal interfacing using a multi channel manner in which alarge quantity of data is simultaneously treated are developed, but amethod of producing a multi-layered optical PCB is not yet suggested, inwhich an element, a waveguide acting as a medium, and a glass fiber areembedded in a PCB.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made keeping in mind theabove problems occurring in the prior art, and an aspect of the presentinvention is to provide a PCB in which various shapes of waveguides fora large surface are embedded, and a method of producing the same, inwhich a core layer cured by UV and a clad layer are coated on the PCBand the core layer is then exposed using an exposing film on which awaveguide pattern is formed.

It is another aspect of the present invention to provide a multi-layeredPCB including a waveguide embedded therein and a method of producing thesame, in which a prepreg is interposed between the waveguide-embeddedPCBs to conduct a lay-up of the PCB and a viahole is then formed andcopperplated to electrically connect layers constituting the resultingPCB to each other.

Additional aspects and/or advantages of the invention will be set forthin part in the description which follows and, in part, will be obviousfrom the description, or may be learned by practice of the invention.

The above and/or other aspects are achieved by providing a PCB in whicha waveguide is embedded, including a substrate, and a lower clad layerformed on the substrate through a predetermined process to allow anoptical signal irradiated thereto to be total-reflected thereby. A corelayer is formed on the lower clad layer through a predetermined processand exposed using an exposing film on which a waveguide pattern isformed to form the waveguide with a predetermined shape therefrom.Furthermore, an upper clad layer is formed on the core layer through apredetermined process to allow the optical signal irradiated thereto tobe total-reflected thereby.

Additionally, the above and/or other aspects are achieved by providing amulti-layered PCB in which the waveguide is embedded. In this regard,the multi-layered PCB is produced by interposing a prepreg between PCBsin which the waveguides are formed to conduct a layup of the PCB,forming via holes to connect layers constituting the resulting PCB toeach other, and copperplating the via holes to form copperplated layersto electrically connect the layers constituting the resulting PCB toeach other.

Moreover, the above and/or other aspects are achieved by providing amethod of producing a PCB in which a waveguide is embedded. At thistime, the method includes a first step of forming a circuit pattern anda target image for alignment on a substrate, a second step of forming alower clad layer on the substrate on which the circuit pattern andtarget image for alignment are formed, a third step of forming a corelayer from which the waveguide with a predetermined shape is to beformed on the lower clad layer, a fourth step of aligning an exposingfilm on which a waveguide pattern with a predetermined shape is formedon the core layer using the target image formed on the substrate, afifth step of exposing the core layer by UV using the exposing film onwhich the waveguide pattern is formed to form the waveguide for a largearea on the lower clad layer, and a sixth step of forming an upper cladlayer on the core layer from which the waveguide is formed.

Further, the above and/or other aspects are achieved by providing amethod of producing a PCB in which a waveguide is embedded. At thistime, the method includes a first step of forming a circuit pattern anda target image for alignment on a substrate, a second step of forming alower clad layer on the substrate on which the circuit pattern andtarget image for alignment are formed, a third step of forming a corelayer from which the waveguide with a predetermined shape is to beformed on the lower clad layer, a fourth step of aligning an exposingfilm on which a waveguide pattern with a predetermined shape is formedon the core layer using the target image formed on the substrate, afifth step of exposing the core layer by UV using the exposing film onwhich the waveguide pattern is formed to form the waveguide for a largearea on the lower clad layer, a sixth step of forming an upper cladlayer on the core layer from which the waveguide is formed, a seventhstep of laminating the PCBs including the waveguides with a prepreginterposed therebetween, and a eighth step of forming through holes ofwhich surfaces are plated with copper, through the PCBs to electricallyconnect layers constituting the PCBs to each other.

BRIEF DESCRIPTION OF THE DRAWINGS

This and other aspects and advantages of the invention will becomeapparent and more readily appreciated from the following description ofthe preferred embodiments, taken in conjunction with the accompanyingdrawing of which:

FIG. 1 is a sectional view of a PCB including a waveguide according tothe first embodiment of the present invention;

FIG. 2 is a sectional view of a PCB including a waveguide according tothe second embodiment of the present invention;

FIG. 3 is a flow chart showing the production of a PCB including awaveguide according to the present invention;

FIG. 4 is a flow chart showing the formation of a circuit pattern and atarget image for alignment on the PCB according to the presentinvention; and

FIGS. 5A to 5M are sectional views illustrating the production of thePCB including the waveguide according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the present preferredembodiments of the present invention, examples of which are illustratedin the accompanying drawing.

According to the first embodiment of the present invention, as shown inFIG. 1, a PCB of the present invention, in which a waveguide with apredetermined shape for a large area is embedded, includes a substrate100, a lower clad layer 200, the waveguide 500, and an upper clad layer400.

At this time, a core layer 300 as will be described later is exposed byUV using an exposing film 800 on which a waveguide pattern is formed toform the waveguide 500 corresponding in shape to the waveguide patternof the exposing film 800 therein.

A copper clad laminate (CCL) may be used as the substrate 100, whichconsists of a dielectric layer 110 made of a dielectric material such asepoxy, and copper clads 120 formed on an upper and a lower side of thedielectric layer 110 using a press and patterned to form a circuitpattern 130 and a target image 140 for alignment.

Alternatively, a resin-coated copper (RCC) may be used as the substrate100, which consists of a dielectric layer 110 made of a dielectricmaterial such as epoxy, and a copper clad 120 formed on any one side ofan upper and a lower side of the dielectric layer 110 using a press andpatterned to form a circuit pattern 130 and a target image 140 foralignment.

The target image 140 functions to correspondingly align a position ofthe waveguide 500 formed in the core layer 300 to a position of theexposing film 800 including the waveguide pattern used to form thewaveguide 500.

The lower clad layer 200 is formed on the substrate 100 on which thecircuit pattern 130 and target image 140 are formed through a coatingand a drying step according to a predetermined process, in detail, alamination, a rolling, or a squeeze printing process, and has slightlysmaller refractivity than the core layer 300 to prevent light irradiatedto the core layer 300 from streaming outside of the core layer 300.

At this time, a liquid-type clad with a polymer structure is coated anddried on the substrate 100 according to the rolling, lamination, screen,or spray process to form the lower clad layer 200 on the substrate 100.

The rolling process includes coating the clad supplied from a vesselcontaining a photo-reactive liquid polymer by a pump on the substrateusing a roller while the substrate on which the circuit pattern andtarget image for alignment are formed is moved using a predeterminedmoving unit.

Additionally, in the case of the lamination process, the clad suppliedfrom a tub-type roll wound by a clad material is coated on the substrateusing a roller to form the clad layer on the substrate when thesubstrate on which the circuit pattern and target image for alignmentare formed is moved using a predetermined moving unit.

Furthermore, according to the screen printing process, the clad materialis coated using a screen printing plate on the substrate on which thecircuit pattern and target image for alignment are formed to form thelower clad layer on the substrate. In detail, the screen printing plateis mounted on the substrate to print various patterns including acorrosion resist, a solder resist, and a symbol mark, as well as a wirepattern on the substrate. Clad and core forming materials are thencoated on the substrate using a squeeze to form the lower and upper cladlayer, and the core layer on the substrate.

As for the spray process, the clad and core forming materials aresprayed on the substrate on which the circuit pattern and target imagefor alignment are formed to form the lower and upper clad layer, and thecore layer on the substrate.

The core layer 300 is formed on the lower clad layer 200 according to apredetermined process, in detail, the lamination, rolling, or squeezeprinting process, and has a higher refractivity than the lower cladlayer 200 to allow the optical signal irradiated through one end of thewaveguide 500 to cause a total-reflection at interfaces of the corelayer 300, lower clad layer 200, and upper clad layer 400, therebytransmitting the optical signal through the core layer 300 into anotherend of the waveguide 500.

Additionally, a liquid polymer, 97% or more transparent, cured by the UVis coated on the lower clad layer 200 according to the lamination,rolling, or squeeze printing process to form the core layer 300 on thelower clad layer 200.

Furthermore, when the core layer 300 is exposed to the UV through theexposing film 800 on which the waveguide pattern corresponding inposition to the target image 140 formed on the substrate 100 is formed,various shapes of waveguides 500 are formed along the waveguide patternformed on the exposing film 800.

The upper clad layer 400 is formed on the core layer 300 in which thewaveguide 500 with a predetermined shape is formed through a coating anda drying step according to a predetermined process, in detail, thelamination, rolling, or squeeze printing process, and has the slightlysmaller refractivity than the core layer 300 to prevent light irradiatedto the core layer 300 from streaming outside of the core layer 300.

At this time, a liquid-type clad with a polymer structure is coated onthe core layer 300 in which the waveguide 500 is formed according to thelamination, rolling, and squeeze printing process to form the upper cladlayer 400 on the core layer 300.

According to the second embodiment of present invention, a method ofproducing a multi-layered PCB in which the waveguide is embedded,includes interposing a prepreg 900 between PCBs in which the waveguidesare formed to conduct a layup of the PCB as shown in FIG. 2, forming viaholes 1000 to connect layers constituting the resulting PCB to eachother, and copperplating the via holes 1000 to form copper-plated layers1100 to electrically connect the layers constituting the resulting PCBto each other.

Hereinafter, a detailed description will be given of the production ofthe PCB in which the waveguide for a large area is embedded according tothe present invention, referring to FIGS. 3 to 5.

FIG. 3 is a flow chart showing the production of a PCB including awaveguide according to the present invention, FIG. 4 is a flow chartshowing the formation of a circuit pattern and a target image foralignment on the PCB according to the present invention, and FIGS. 5A to5M are sectional views illustrating the production of the PCB includingthe waveguide according to the present invention.

Referring to FIG. 3, a circuit pattern and a target image for alignmentare formed on a substrate 100 in operation 100.

In FIGS. 5A to 5M, there is illustrated a procedure of forming thecircuit pattern 130 and target image 140 for alignment on a copper clad120 of the substrate 100.

With reference to FIGS. 4 and 5A, a copper clad laminate or aresin-coated copper (not shown) including a dielectric layer 110 and acopper clad 120 formed on an upper and a lower side thereof or on anyone side of the upper and lower side thereof is used as the substrate100 in operation 101.

Referring to FIG. 5B, a dry film (D/F) 600 is layered on the copper clad120 of the copper clad laminate or resin-coated copper 100 to transcribethe circuit pattern 130 and target image 140 for alignment of FIG. 5F onthe copper clad 102 in operation 102.

Turning to FIG. 5C, after the dry film (D/F) 600 is layered on thecopper clad 120, the dry film 600 is exposed by UV using an artwork film700 from which the circuit pattern and target image for alignment areformed in operation 103.

As shown in FIG. 5D, a portion of the dry film 600 is dissolved andremoved, which occupies an area except for the other portion of the dryfilm 600 exposed to the UV to be cured in operation 104.

Referring to FIG. 5E, the copper clad 120 is subjected to an etchingprocess in operation 105. At this time, a portion of the copper clad 120is coated with a portion of the dry film 600 not removed.

In FIG. 5F, after a portion of the copper clad 120 not coated with aportion of the dry film 600 cured by the UV is etched and removed, thedry film 600 is separated from the copper clad 120 to construct thecircuit pattern 130 and target image 140 for alignment having apredetermined shape on the copper clad laminate or resin-coated copper100 in operation 106.

The lower clad layer is then formed on the substrate 100 as a means tocover the circuit pattern and target image for alignment in operation200.

In other words, as shown in FIG. 5G, a clad material is coated on thecircuit pattern 130 and target image 140 for alignment on the substrate100 according to a predetermined process, for example, the lamination,rolling, screen printing, or spray process.

In FIG. 5H, the clad material coated on the circuit pattern 130 andtarget image 140 for alignment on the substrate 100 is dried and curedat predetermined temperatures to form the lower clad layer 200 on thesubstrate 100.

That is to say, a liquid clad material with a polymer structure iscoated on the substrate 100 and dried according to the lamination,rolling, screen printing, and spray process to form the lower clad layer200 on the substrate 100.

In this regard, the lower clad layer 200 has slightly lower refractivitythan the core layer 300 through which an optical signal passes toprevent light irradiated to the core layer 300 from streaming outside ofthe core layer 300.

After the lower clad layer 200 is formed on the circuit pattern 130 andtarget image 140 on the substrate 100, the core layer 300 is formed onthe lower clad layer 200 to form the waveguide with a predeterminedshape therein in operation 300.

In detail, a predetermined core material is attached and coated on thelower clad layer 200 according to a predetermined process, for example,any one process of the lamination, rolling, screen printing, and sprayprocess to form the core layer 300 on the lower clad layer 200 as shownin FIG. 5I.

At this time, a liquid polymer, 97% or more transparent, cured by the UVis coated on the lower clad layer 200 according to the lamination,rolling, screen printing, or spray process to form the core layer 300 onthe lower clad layer 200.

Furthermore, the core layer 300 has the higher refractivity than thelower clad layer 200 to allow the optical signal irradiated through oneend of the waveguide 500 to cause a total-reflection at interfaces ofthe core layer 300 and lower clad layer 200, thereby transmitting theoptical signal through the core layer 300 into another end of thewaveguide 500.

As shown in FIG. 5J, after the core layer 300 is formed on the lowerclad layer 200, the exposing film 800 on which the waveguide patternwith a predetermined shape is formed is aligned on the core layer 300 sothat the exposing film 800 corresponds in a position to the target image140 formed in the copper clad 120 on the substrate 100 in operation 400.

Turning to FIG. 5K, the core layer 300 is exposed by the UV using theexposing film 800 on which the waveguide pattern is formed in operation500.

At this time, as shown in FIG. 5L, a portion of the core layer 300 whichoccupies an area except for the other portion of the core layer 300cured by the UV passing through the exposing film 800 is removed to formthe waveguide 500 having the corresponding shape to the waveguidepattern formed on the exposing film 800.

Referring to FIG. 5M, after the core layer 300 is exposed by the UV toform the waveguide 500 with a predetermined shape, an upper clad layer400 is formed on the core layer 300 in which the waveguide 500 is formedin operation 600.

In this regard, the clad material is coated on the core layer 300 inwhich the waveguide 500 with a predetermined shape is formed accordingto a predetermined process, for example, any one process of thelamination, rolling, and squeeze printing process, and dried atpredetermined temperatures to form the upper clad layer 400 with thepredetermined refractivity on the core layer 300, thereby accomplishingthe PCB in which the waveguide is embedded.

At this time, the upper clad layer 400 has the slightly smallerrefractivity than the core layer 300 through which the optical signalpasses to prevent light irradiated to the core layer 300 from streamingoutside of the core layer 300.

Furthermore, a method of producing the PCB in which the waveguide 500 isembedded according to the present invention, further includesinterposing a prepreg 900 between the PCBs having the waveguides 500,and forming through holes 1000 of which surfaces are plated with copperto electrically connect layers constituting the PCB to each other.

As apparent from the above description, the present invention provides aPCB in which waveguides with various shapes for a large area areembedded, and a method of producing the PCB. In this regard, the methodincludes forming a core layer cured by UV and a clad layer on the PCB inwhich a circuit pattern is formed, and exposing the core layer by the UVusing an exposing film on which a waveguide pattern with a predeterminedshape is formed.

Additionally, the present invention provides a method of producing amulti-layered PCB in which a waveguide is embedded, includinginterposing a prepreg between PCBs on which the waveguides are formed toconduct a layup of the substrate, forming via holes to connect layersconstituting the resulting substrate to each other, and copperplatingthe via holes to form copperplated layers to electrically connect thelayers constituting the substrate to each other.

Furthermore, the present invention is advantageous in that a targetimage for alignment on the substrate serves to correspondingly alignpositions of the waveguide formed in the core layer and a film on whichthe waveguide pattern is formed.

The present invention has been described in an illustrative manner, andit is to be understood that the terminology used is intended to be inthe nature of description rather than of limitation. Many modificationsand variations of the present invention are possible in light of theabove teachings. Therefore, it is to be understood that within the scopeof the appended claims, the invention may be practiced otherwise than asspecifically described.

1. A printed circuit board in which a waveguide is embedded, comprising:a substrate on which a circuit pattern and a target image each having apredetermined shape are formed; a lower clad layer formed on thesubstrate, said circuit pattern, and said target image through apredetermined process to allow an optical signal irradiated thereto tobe total-reflected thereby; a core layer formed on the lower clad layerthrough a predetermined process and exposed using an exposing film onwhich a waveguide pattern is formed to form to define the waveguide witha predetermined shape for a large area therefrom; and an upper cladlayer formed on the core layer through a predetermined process to allowthe optical signal irradiated thereto through said waveguide to betotal-reflected thereby; wherein the substrate comprises a copper cladlaminate (CCL) including a dielectric layer and copper clads formed onan upper and a lower side of the dielectric layer using a press, thecopper clads being patterned to form the circuit pattern and targetimage each having the predetermined shape therefrom.
 2. The printedcircuit board as set forth in claim 1, wherein the lower clad layer isformed on the substrate through any one process of a lamination, arolling, a screen printing, and a spray process.
 3. The printed circuitboard as set forth in claim 1, wherein the core layer is formed on thelower clad layer through any one process of a lamination, a rolling, ascreen printing, and a spray process.
 4. The printed circuit board asset forth in claim 1, wherein the upper clad layer is formed on the corelayer from which the waveguide is formed through any one process of alamination, a rolling, a screen printing, and a spray process.
 5. Theprinted circuit board as set forth in claim 1, wherein a polymer-typeclad is coated on the substrate and core layer, and dried to form thelower and upper clad layer on the substrate and core layer.
 6. Theprinted circuit board as set forth in claim 1, wherein a polymer-typecore material, 97% or more transparent, cured by UV is coated on thelower clad layer to form the core layer on the lower clad layer.
 7. Aprinted circuit board in which a waveguide is embedded, comprising: asubstrate on which a circuit pattern and a target image each having apredetermined shape are formed; a lower clad layer formed on thesubstrate, said circuit pattern, and said target image through apredetermined process to allow an optical signal irradiated thereto tobe total-reflected thereby; a core layer formed on the lower clad layerthrough a predetermined process and exposed using an exposing film onwhich a waveguide pattern is formed to form to define the waveguide witha predetermined shape for a large area therefrom; and an upper cladlayer formed on the core layer through a predetermined process to allowthe optical signal irradiated thereto through said waveguide to betotal-reflected thereby; wherein the substrate comprises a resin-coatedcopper (RCC) including a dielectric layer and a copper clad formed onany one side of an upper and a lower side of the dielectric layer usinga press, the copper clad being patterned to form the circuit pattern andtarget image each having the predetermined shape therefrom.
 8. Theprinted circuit board as set forth in claims 1 or 7, wherein the targetimage formed on the substrate correspondingly aligns a position of thewaveguide formed on the core layer to a position of the exposing film onwhich the waveguide pattern is formed.
 9. A printed circuit board inwhich a waveguide is embedded, comprising: a substrate on which acircuit pattern and a target image each having a predetermined shape areformed; a lower clad layer formed on the substrate, said circuit patternand said target image to allow an optical signal irradiated thereto tobe total-reflected thereby; a core layer formed on the lower clad layerand exposed using an exposing film on which a waveguide pattern isformed to form the waveguide with a predetermined shape; and an upperclad layer formed on the core layer to allow the optical signal throughsaid waveguide to be total-reflected thereby; wherein the substratecomprises a copper clad laminate (CCL) including a dielectric layer andcopper clads formed on an upper and a lower side of the dielectric layerusing a press, the copper clads being patterned to form the circuitpattern and target image.
 10. A printed circuit board comprising: asubstrate having a top surface with a circuit pattern formed of anelectrically conductive material; a lower clad layer formed on andcontacting said top surface and said circuit pattern, said lower cladlayer being made of a first light conducting material having a firstrefractivity; a waveguide formed on said lower clad layer and made of asecond light conducting material having a second refractivity that ishigher than said first refractivity to confine light being transmittedthrough said waveguide; and an upper clad layer formed on said waveguideand said first lower clad layer, said upper clad layer and said lowerclad layer cooperating to surround said waveguide, wherein saidsubstrate is provided on its upper surface with a target image for saidwaveguide, said target image is made of the same electrically conductivematerial as said circuit pattern; wherein the substrate comprises acopper clad laminate (CCL) including a dielectric layer and copper cladsformed on an upper and a lower side of the dielectric layer using apress, the copper clads being patterned to form the circuit pattern. 11.The printed circuit board of claim 10 wherein said upper clad layer ismade of a material having a smaller refractivity then said waveguide,said upper and lower clad layers cooperating to totally reflect lightinto said waveguide.
 12. The printed circuit board of claim 10 whereinsaid substrate has a bottom surface with another circuit pattern.